Due to specific reasons* we do recommend that your clients submit either via email, direct upload or the Mobile app rather than using DropBox.
To get the best advantage, this DropBox account could be something especially created for you and your clients items, instead of using a personal DropBox account.
Additionally, your clients can link themselves with their own DropBox accounts and upload items too:
*Unfortunately, our DropBox integration is quite fragile and re-naming or moving folders can break it. If we are unable to extract any files they will be left in the target folder and you will receive a notification email.